I've had this problem in awhile, in one of my pages http://pinoguin.com/pnews.html the very bottom container of the news to the right - where you can see the curved borders has been cut off. Any idea what could be causing this? It seems to only appear when select content are inserted.. but I dunno which one and it's not supposed to do that!
Use a universal reset. You may have to alter your margins for paragraphs, etc.. but this makes it more cross browser compatible since every browser gives different value for margin or padding to various elements.. better to reset it to 0.